This invention relates to a photopolymerizable epoxy resin composition having a novel composition, more particularly to an epoxy resin composition having good photo-curability, less corrosive properties and excellent electrical characteristics.
In the specifications of U.S. Pats. Nos. 3,205,156 and No. 3,708,296, there are disclosed light-susceptible epoxy resin compositions containing an aryldiazonium salt and an aryldiazonium salt of a halogen-containing complex anion, respectively. These compositions are restricted in their availabilities for reasons of (1) less thermal stability, (2) spectral responses limited to an unltraviolet region of spectrum, and (3) the occurrence of pinholes and air bubbles in a cured composition due to the generation of nitrogen during photopolymerization.
Also when oxetane or a mixture of oxetane and an epoxy resin is photopolymerized by the use of aforesaid aryldiazonium salt, the same problem as mentioned above will arise (see the specification of U.S. Pat. No. 3,835,003).
Some patents (see specifications of U.S. Pat. Nos. 3,711,390, 3,711,931, 3,816,278, 3,817,850 and 3,817,845) disclose methods for stabilizing mixtures of diazonium salts and epoxides. These methods, however, are unsatisfactory for several reasons. For example, with regard to their stability, its good state can merely be retained for so short a period as to be represented by the unit of days, and the addition of a stabilizer, which is a non-reactive material, will contaminate a desired composition, with the consequence that this added material will soften a product thereof and will deteriorate a photo-setting speed.
Further, in the specification of U.S. Pat. No. 3,450,613, there is disclosed a photopolymerizable epoxy resin composition comprising a reaction product of an epoxy resin prepolymer and an ethylenically unsaturated organic acid, a light-susceptible agent and optionally a poly-functional acid or hydrochloric acid.
The gelation of this composition can be accomplished by the photopolymerization of an ethylenically unsaturated portion in the reaction product when exposed to ultraviolet rays, but for the sake o the complete cure of the composition, it is necessary that an epoxy resin portion of the composition is caused to carry out a curing reaction. For this purpose, it is finally required to give a thermal treatment to the composition. In other words, in order to accomplish the complete polymerization (curing) of this composition, both light and heat are needful. For this reason, applicable fields of the composition are inevitably limited. In addition thereto, this composition has the problems of being sensitive to enzymes and being low in thermal stability.
On the other hand, as photo-setting catalysts for the photopolmerizable epoxy resin composition, complexes represented by the following formula are known: ##STR1## wherein Ar is a phenyl group or the like;
X is an iodine atom, sulfur atom diazo group of the like; and PA1 Y is a BF.sub.4, PF.sub.6, AsF.sub.6, SbF.sub.6 or the like.
[see, for example, Macromolecules, Vol. 10, p. 1307 (1977); Journal of Radiation Curing, Vol. 5, p. 2 (1978); Journal of Polymer Science, Polymer Chemistry Edition, Vol. 17, p. 2877 (1979); Ibid. Vol. 17, p. 1047 (1979); Journal of Polymer Science, Polymer Letters Edition, Vol. 17, p. 759 (1979); Japanese Provisional Patent Publication No. 65219/1980; U.S. Pat. No. 4,069,054; and British Pats. Nos. 1,516,511 and 1,518,141.]
However, when the photopolymerization of the epoxy resin is carried out with this photo-setting catalyst, the cured material will be improved in mechanical properties, but on the other hand, if used in the field of electric applicances, the cured material will inevitably deteriorate in electrical insulating properties and will corrode peripheral parts, because the added catalyst functions as an ionic impurity.